This invention relates to a method and apparatus for improving the performance of pumping and thrust- or lift-augmenting ejectors, and, in general, of devices in which a fluid is induced to flow through direct exchanges of momentum and energy with another flow.
Direct flow induction--the direct transfer of momentum and energy from one fluid stream to another--generally involves both a dissipative and a non dissipative component, the latter being provided by the work of interface pressure forces. For these forces to do work, the interfaces on which they act must be allowed or imparted a transverse motion. Therefore, the nondissipative component of energy transfer can take place only where the interacting flows are nonsteady. It does not follow, however, that the nonsteady modes of flow induction are always to be preferred to the steady ones. In the first place, interface pressure forces may act in a direction to oppose, rather than to promote, the desired transfer of momentum and/or energy; and in the second place, the flow losses associated with the generation of the required nonsteadiness are often large--large enough, in some cases, to outweigh whatever benefit could otherwise be derived from the subsequent utilization of the nonsteadiness so generated.
A notable exception in this respect is the class of those mechanisms which transform a steady-flow interaction into a nonsteady one by the simple artifice of utilizing it in a frame of reference other that the unique one in which it is steady. Flow induction mechanisms of this class are exemplified by the rotary jet (U.S. Pat. No. 3,046,732), which is an ejector in which the driving ("primary") jets are made to issue out of slanted nozzles on the periphery of a free-spinning rotor. The rotor, and with it the interfaces between the primary jets and the surrounding ("secondary") fluid, are thus made to rotate, thereby allowing the interface pressure forces to do work. Theory predicts, and experiments have confirmed, a consistently and significantly higher energy transfer efficiency for the rotary-jet ejector, all else being equal, than for its steady-flow counterpart.
An important drawback of the rotary jet relative to the conventional steady-flow ejector is its poor adaptability to axially symmetric interaction spaces. Filling such spaces with clusters of rotary jets could not fully solve the problem of space utilization and may well entail adverse interference effects. A far more promising approach is offered by the concept discussed in the following paragraphs.